PROJECT SUMMARY/ABSTRACT Delirium is a serious but under-studied complication of stay in the pediatric intensive care unit (PICU). Sleep disruption is frequently observed in children with delirium, and circadian rhythm dysregulation due to poor sleep quality during critical illness is one proposed pathway to delirium. Children admitted to the PICU experience multiple environmental exposures with the potential to disrupt sleep, including excessive light and sound and frequent caregiving. The scientific premise of this study is that modifiable characteristics of the pediatric critical care environment, including excessive light and sound and frequent caregiving, contribute to sleep disruption and thus have a physiological effect that may lead to delirium. The primary purpose of this research training plan is to develop a measurement framework that illustrates the relationship between modifiable characteristics of the pediatric critical care environment (i.e., light and sound exposure, caregiving frequency), sleep disruption, and delirium in a critically ill pediatric sample 5 years of age and younger. This observational, repeated measures study will accomplish the following specific aims: (1) Describe selected modifiable characteristics of the pediatric critical care environment, sleep disruption, and the incidence and duration of delirium across a 5-day period in a sample of 20 critically ill children 5 years of age and younger. (2) Examine the relationships among selected modifiable characteristics of the pediatric critical care environment, sleep disruption, and the incidence and duration of delirium. (2a) Examine the mediating effect of sleep disruption on the relationship between selected characteristics of the pediatric critical care environment and the incidence and duration of delirium. This study is among the first to explore the association between sleep disruption and delirium in critically ill children. This aligns with the mission of the NINR Strategic Plan in Symptom Science to understand biological and behavioral aspects of symptoms. Once validated, the measurement framework developed in this study will be used to design and test environmental modification and/or sleep promotion interventions to prevent delirium in pediatric populations. The long-term goal of this program of research is to improve the neurocognitive symptom management and long-term outcomes of critically ill children by optimizing the pediatric critical care environment. This 3-year pre-doctoral training plan has the following goals: (1) Build understanding and proficiency in quantitative research methods and statistical analyses. (2) Acquire the necessary skills and knowledge to evaluate how exposures in the pediatric intensive care environment contribute to the incidence and duration of delirium in critically ill children. (3) Advance scientific understanding of pediatric delirium through scholarly writing and dissemination of research findings. (4) Develop professionally in preparation for a faculty position at a research-intensive academic institution. The diverse educational and professional experiences proposed in this training plan will support development of the applicant into an early-stage nurse investigator.